In pathological diagnosis, quantification of the expression level of biological materials excessively expressed in tissue sections can provide very important information for prognostic prediction and the following treatment planning. Such quantification of biological materials involves analysis of a specific biological material in a region of interest, which is a region selected for analysis in a tissue section. For such quantification of biological materials, therefore, there has been a demand for development of techniques capable of accurately quantifying biological materials and accurately extracting a region of interest.
Thus, for example, Patent Literature 1 describes a method that includes staining tissue samples by immunohistochemical staining using a fluorescent material and analyzing the expression level of a specific protein based on the number of bright fluorescent spots in a specified region of interest. The use of a fluorescent material in immunostaining allows a specific protein to be observed as bright fluorescent dot-like spots. Therefore, this makes it possible to quantify a specific protein with high accuracy even by an immunohistochemical staining method relatively simpler than fluorescence in situ hybridization and other techniques.